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# Mechanical Comprehension Review for ASVAB Power Practice Problems (page 2)

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Updated on Aug 12, 2011

1. c.   A pulley system of this type has a mechanical advantage of 2. So, a 250-pound weight can be lifted with 250 pounds ÷ 2 = 125 pounds.
2. a.   The density of mercury is strongly temperature dependent. When placed in hot liquid, mercury expands by a known amount, forcing small amounts of liquid mercury up the thermometer.
3. a.   w1 × d1 = w2 × d2. 120 pounds × 11 feet = w2 × 6 feet. Solving for w2 gives 220 pounds.
4. c.   The crank is moving counterclockwise, meaning that when it is pointing downward it is moving away from the piston (to the right). So, the piston will be in a central position. Since the crank is moving to the right, the piston will also be moving to the right.
5. b.   12 miles ÷ 1.5 hours = 8 miles per hour.
6. a.   The mechanical advantage (MA) of a ramp is determined by the length of the ramp, l, divided by the height gained, h. In this case, MA = = 25 feet ÷ 10 feet = 2.5. The force required to pull a 300-pound block up a ramp is 300 pounds ÷ 2.5 = 120 pounds.
7. a.   The force constant of the spring is 10 pounds ÷ 8 inches = 1.25 pounds per inch. Using the equation, F = kx, we have 15 pounds = 1.25 pounds per inch × x. Solving for x gives 12 inches.
8. c.   If 18 turns move the nut 1.2 inches, there are 18 turns ÷ 1.2 inches = 15 threads per inch.
9. b.   Mechanical advantage = output force ÷ input force. Here, 40 pounds of force is input to lift a 120-pound load. The mechanical advantage is 120 ÷ 40 = 3.
10. a.   The mechanical advantage of this pulley system is 4. The force required to lift the 300-pound load is 300 pounds ÷ 4 = 75 pounds.
11. b.   Gear 1 turning clockwise will cause gears 2 and 4 to turn counterclockwise. Gear 3 will be the only other gear that turns clockwise.
12. d.   When a submarine fills its tanks with water it becomes heavier, which decreases its buoyancy and increases its density. The volume of the submarine remains unchanged through the entire process.
13. d.   Because pulley system B has a mechanical advantage of 2, the rope must be pulled twice as far as pulley system A to do the same amount of work: 2 × 10 feet = 20 feet.
14. a.   If a vertical line is drawn straight down from the center of gravity, only the line for truck A reaches the ground outside of the truck's tires. This makes the truck unstable.
15. a. Cable A is attached to the arm closest to the crane. Therefore, it has the weakest mechanical advantage and so will be under the most strain to support the weight of the arm.
16. a.   The total volume of the block is 2 inches × 2 inches × 5 inches = 20 inches3. Its density is 0.3 pounds per cubic inch, so its total weight must be 20 inches3 × 0.3 pounds per inch3 = 6 pounds.
17. d.   w1 × d1 = w2 × d2. Talia is 18 feet away from the pivot point. 90 pounds × 8 feet = 10 feet × w2. Solving for w2 gives 50 pounds.
18. b.   Wood is the best choice. All other objects are very dense and will quickly sink. Wood offers a lower density while still remaining strong enough to function as a raft.
19. d.   Each full turn of the pedals will turn the rear wheel 48 ÷ 12 = 4 revolutions. If the pedals are turning at 90 rpm, the rear wheel will move at 4 × 90 rpm = 360 rpm.
20. c.   Pulley systems A and B offer a mechanical advantage of 2, whereas pulley system C offers a mechanical advantage of 1. In A and B, the rope used to raise the weight moves 2 feet for every 1 foot the pulley is raised, whereas in C the rope used to raise the weight moves 1 foot for every foot the weight is raised.
21. b.   w1 × d1 = w2 × d2. 50 pounds × 8 feet = 100 pounds × d2. Solving for d2 gives 4 feet.
22. b.   In this pulley system, the weight of the load is shared over 2 cables and so the mechanical advantage is 2.
23. b.   Since all materials occupy the same volume, the material with the greatest density will be the heaviest. Lead is an extremely dense material and is much denser than all other options.
24. c.   Since pulley A is 2.5 times greater in diameter than pulley B, each revolution of A will lead to 2.5 revolutions of B. If A rotates at 50 rpm, then B will rotate at 50 rpm × 2.5 = 125 rpm.
25. b.   If gear 3 turns counterclockwise, it will lead to its neighboring gears (2 and 4) to turn clockwise.